In the field of hydronics generally, temperature-controlled solenoid valves have been known since at least as early as 1916 when U.S. Pat. No. 1,167,815 issued to E. E. Gold. Gold disclosed a thermostat which was adjustable to be set to a preselected temperature so that when a sufficient change in temperature occurred, the thermostat acted as a switch to open or close a solenoid valve control circuit. When this circuit was closed by the thermostatic switch, power was supplied to a solenoid valve which energized the valve and caused the valve to close. When the circuit was opened, the power was discontinued to the solenoid which when de-energized thereby allowed the valve to open. When the valve was thus opened, temperature-conditioned water flowed through the valve to a radiator or a similarly associated temperature conditioning and/or circulating device to provide heating (or cooling) to a room or a like hydronic zone with which the thermostat and radiator was associated.
Numerous advancements have since been introduced to the art, particularly toward the reduction of certain noises associated with valve operations. These later teachings have included mechanical and/or electrical devices for noise reduction. Examples of such devices include different types of springs, dampers, TEFLON seats, relays, rectifiers, thyristors, zener diodes, and pulse-generating circuits. However, there still appears to be a need for improvements particularly in providing devices which reduce water hammer and solenoid humming in user-friendly and inexpensive devices.
Moreover, many conventional zone valves have other drawbacks as well. For example, many prior art valves require a three-wire thermostat with complicated wiring between the power supply, the thermostat and the solenoid valve or, they require a separate relay to convert the three-wire thermostats to less complicated two-wire thermostat installations. A conventional three-wire thermostat zone valve setup is shown, for example, in the U.S. patent to L Troy (U.S. Pat. No. 3,610,523). In the Troy system, each independent thermostat has three electrical contacts which comprise, in essence, a single-pole, double-throw ("SPDT") switch. In use, one contact is for the common line (also identified by the letter R in the conventional R, W, B lettering scheme) from the power source, the other two are for two distinct sub-circuits; namely a solenoid sub-circuit and a circulator sub-circuit. When switched to place the common line in contact with and close the solenoid sub-circuit, power is then supplied to a solenoid valve to close the valve. On the other hand, when the thermostat switch is moved by the appropriate temperature change to open the solenoid sub-circuit, the power to the solenoid is stopped which allows the valve to open. A still further effect of a sufficient, preselected temperature change is to connect the common line with the circulator sub-circuit to close that sub-circuit. When this sub-circuit is closed, power is provided to the circulator and/or boiler relay which causes the motor and pump to circulate the temperature conditioned water through the hydronic system. This is demand circulation.
Even so, two-wire thermostatic connections to solenoid valves are preferable because they offer greater simplicity in the wiring of such systems. However, this has heretofore been unavailable with the demand circulation functionality of a three-wire thermostat in a Troy-type of system. Therefore, the provision of a temperature-activated solenoid control which enables demand circulation in a simple two-wire thermostat wiring system would be a distinctive achievement.